Technical Note

The estimates in this report were obtained from the
Current Population Survey (CPS), a national monthly
sample survey of approximately 60,000 households,
which provides a wide range of information on the labor
force, employment, and unemployment. Earnings and union
affiliation data are collected from one-fourth of the CPS
monthly sample. The survey is conducted for the U.S. Bureau
of Labor Statistics (BLS) by the U.S. Census Bureau, using
a scientifically selected national sample with coverage in all
50 States and the District of Columbia.

Material in this report is in the public domain and may be
reproduced without permission. This information is available
to sensory-impaired individuals on request. Voice phone:
(202) 691-5200; Federal Relay Service: 1-800-877-8339.

Reliability of the Estimates

Statistics based on the CPS are subject to both sampling and
nonsampling error. When a sample, rather than an entire
population, is surveyed, there is a chance that the sample
estimates may differ from the “true” population values they
represent. The exact difference, or sampling error, varies
depending on the particular sample selected, and this variability
is measured by the standard error of the estimate.
There is about a 90-percent chance, or level of confidence,
that an estimate based on a sample will differ by no more than
1.6 standard errors from the true population value because
of sampling error. BLS analyses generally are conducted at
the 90-percent level of confidence.

All other types of error are referred to as nonsampling
error. Nonsampling error can occur for many reasons, including
the failure to sample a segment of the population,
inability to obtain information for all respondents in the
sample, inability or unwillingness of respondents to provide
correct information, and errors made in the collection or processing
of data. CPS data also are affected by nonsampling
error. The full extent of nonsampling error is unknown, but
special studies have been conducted to quantify some sources
of such error in the CPS. For further discussion of the reliability
of data from the CPS and information on estimating
standard errors, see the Household Data technical documentation
provided at http://www.bls.gov/cps/documentation.htm#reliability.

Concepts and Definitions

Concepts used in this report are defined below.

Civilian noninstitutional population. The civilian noninstitutional
population includes people 16 years of age and
older residing in the 50 States and the District of Columbia
who are not confined to institutions (for example,
correctional facilities and residential nursing and mental
health care facilities) and who are not on active duty in
the Armed Forces.

Civilian labor force. This group comprises all people classified
as employed or unemployed.

Employed persons. Employed persons are those who, during
the survey week, (a) did any work at all as paid civilians; (b)
worked in their own business or profession or on their own
farm; (c) worked 15 hours or more as unpaid workers in a
family business; or (d) were temporarily absent from their jobs
because of illness, vacation, bad weather, or another reason.

Unemployed persons. Unemployed persons are those who
had no employment during the survey week, were available
for work at that time, and made specific efforts to find employment
sometime in the prior 4 weeks. Workers laid off
from their former jobs and awaiting recall did not need to be
looking for work to be classified as unemployed.

Civilian labor force participation rate. This rate is the civilian
labor force as a percent of the civilian noninstitutional
population.

Employment-population ratio. This ratio represents the
proportion of the population that is employed.

Unemployment rate. This rate represents the number of
unemployed persons as a percent of the civilian labor force.

Race. White, Black or African American, and Asian are terms
used to describe race. People in these categories are those
who selected that race group only. Data for the remaining
race categories—American Indian or Alaska Native, Native
Hawaiian or Other Pacific Islanders, and people who selected
more than one race category—are included in totals but are
not shown separately because the number of survey respondents
was too small to develop estimates of sufficient quality
for publication. In the survey process, race is determined by
the household respondent.

Hispanic or Latino ethnicity. This term refers to people
who identified themselves in the survey as being Spanish, Hispanic, or Latino. People whose ethnicity is identified as
Hispanic or Latino may be of any race.

Family. A family is a group of two or more people residing
together who are related by birth, marriage, or adoption.
Families are classified either as married-couple families or
as families maintained by women or men without spouses.
Families include those with children under 18 in the home
and those without children under 18.

Self-employed workers. Self-employed workers are those
who work for profit or fees in their own business, profession,
trade, or farm. Unincorporated self-employed are included in
the self-employed category. Self-employed workers whose
businesses are incorporated are included with wage and
salary workers.

Wage and salary workers. These are workers who receive
wages, salaries, commissions, tips, payment in kind, or piece
rates. This includes employees in both the private and public
sectors. Union membership and earnings data of wage and
salary workers exclude all self-employed workers, both those
with incorporated businesses and those with unincorporated
businesses.

Hourly paid workers. Workers who are paid an hourly wage
are a subset of wage and salary workers. Historically, workers
paid an hourly wage have made up approximately three-fifths
of all wage and salary workers. Estimates of median usual
weekly earnings in this report are based on the earnings of
all workers—those paid by the hour and those paid a salary
or on some other basis.

Usual weekly earnings. Data are collected on wages and
salaries before taxes and other deductions and include any
overtime pay, commissions, or tips usually received (at the
principal job in the case of multiple jobholders). Earnings of
self-employed workers are excluded, regardless of whether
their businesses are incorporated. Prior to 1994, respondents
were asked to report earnings per week. Since January 1994,
respondents have been asked to identify the easiest way for
them to report earnings (hourly, weekly, biweekly, twice
monthly, monthly, annually, or other) and how much they
usually earn in the reported period. Earnings reported on a
basis other than weekly are converted to a weekly equivalent.
The term “usual” is as perceived by the respondent. If the
respondent asks for a definition of usual, interviewers are
instructed to define the term as “more than half the weeks
worked during the past 4 or 5 months.”

Median weekly earnings. The median is the amount that
divides a given earnings distribution into two equal groups:
one having earnings above the median and the other having
earnings below the median. The BLS estimating procedure
for determining the median of an earnings distribution places
each reported or calculated weekly earnings value into a $50-wide interval that is centered on a multiple of $50. The
value of the median is estimated through a linear interpolation
of the interval in which the median lies. Over-the-year
changes in the medians for specific groups may not necessarily
be consistent with the movements estimated for the
overall group boundary. The most common reasons for this
possible anomaly follow: (1) There could be a change in the
relative weights of the subgroups. For example, the medians
of both 16- to 24-year-olds and those 25 years and over may
rise, but if the lower earning 16-to-24 age group accounts
for a greatly increased share of the total, the overall median
could actually fall. (2) There could be a large change in the
shape of the distribution of reported earnings. This could be
caused by survey observations that are clustered at rounded
values, for example, $300, $400, or $500. An estimate lying
in a $50-wide centered interval containing such a cluster, or
“spike,” tends to change more slowly than one in other intervals.
Consider, for example, the calculation of the median
for a multipeaked distribution that shifts over time. As such
a distribution shifts, the median does not necessarily move
at the same rate. Specifically, the median takes relatively
more time to move through a frequently reported interval but,
once above the upper limit of such an interval, it can move
relatively quickly to the next frequently reported earnings
interval. BLS procedures for estimating medians mitigate
such irregular movements of the measures; however, users
should be cautious of these effects when evaluating short-term
changes in the medians, and in ratios of the medians.

Hours at work. These are the actual hours worked (at all
jobs) during the survey reference week. For example, people
who normally work 40 hours a week but were off during the
Columbus Day holiday would be reported as working 32
hours, even if they were paid for the holiday.

Usual hours, or usual full- or part-time status. Data on people
“at work” exclude those who were temporarily absent from
a job and therefore classified in the zero-hours worked category,
“with a job but not at work.” These are workers who
were absent from their jobs for the entire week for reasons
such as bad weather, vacation, illness, or involvement in a
labor dispute. To differentiate a personís normal schedule
from his or her activity during the reference week, workers
also are classified according to their usual full- or part-time
status. In this context, full-time workers are those who usually
work 35 hours or more (at all jobs combined) per week.
This group includes workers who worked less than 35 hours
in the reference week for either economic or noneconomic
reasons and those who were temporarily absent from work.
Similarly, part-time workers are those who usually work less
than 35 hours per week (at all jobs), regardless of the number
of hours worked in the reference week. This may include
some people who actually worked more than 34 hours in
the reference week, as well as those who were temporarily
absent from work.

Occupation and industry. This information applies to the job
held during the reference week. People with two or more jobs
are classified in the occupation and industry in which they
worked the greatest number of hours. The occupational
and industry classification of CPS data is based on the
2002 Census Occupational Classification system and the
2007 Census Industrial Classification system, which are
derived from the 2000 Standard Occupation Classification
(SOC) and the 2007 North American Industry
Classification (NAICS). Additional information about
these classifications is available online at http://www.
bls.gov/cps/cpsoccind.htm.

Work experience. These data reflect work activity during the
calendar year and are obtained from the Annual Social and
Economic Supplement (ASEC) to the Current Population
Survey. Estimates of people who worked were based on
“yes” responses to the following questions in the ASEC:
“Did you work at a job or business at any time during [the
survey reference year]?” or “Did you do any temporary,
part-time, or seasonal work even for a few days during [the survey reference year]?” Since the reference period is
a full year, the number of people with some employment
or unemployment greatly exceeds the average levels for
any given month, which are based on a 1-week reference
period, and the corresponding annual averages of monthly
estimates.

Poverty classification. Poverty statistics presented in this
report are based on definitions developed by the Social
Security Administration in 1964 and revised by the Federal
interagency committees in 1969 and 1981. These definitions
originally were based on the Department of Agricultureís
Economy Food Plan and reflected the different consumption
requirements of families, based on factors such as family size
and the number of children under 18 years of age. The actual
poverty thresholds vary in accordance with the makeup of the
family. Poverty thresholds are updated each year to reflect
changes in the Consumer Price Index for All Urban Consumers
(CPI-U). The thresholds do not vary geographically. For
more information on poverty data and thresholds, see http://
www.census.gov/hhes/www/poverty/poverty.html.